1. Field of the Invention
The present invention relates to a retractable lens barrel, and in particular to a zooming mechanism in which cam pins are engaged with cam grooves.
2. Description of the Related Art
Conventionally, optical apparatuses such as digital cameras having a zoom lens barrel of a retractable type (hereinafter referred to as a retractable lens barrel) have been in widespread use. As a zoom lens extension mechanism in a retractable lens barrel, there has been known a drive mechanism that engages cam pins formed in the lens barrel with cam grooves formed in a movable cam ring, and rotatively drives the movable cam ring to move the lens barrel forward and backward in a direction of an optical axis along the cam grooves. In such a zoom lens extension mechanism in which cam pins are engaged with cam grooves, it is necessary to prevent the cam pins from slipping off the cam grooves to render the lens barrel incapable of moving forward and backward when external force is applied.
As this slip-off preventive technique, there has been proposed, for example, a technique described in Japanese Laid-Open Patent Publication (Kokai) No. 2005-128188. According to the technique described in Japanese Laid-Open Patent Publication (Kokai) No. 2005-128188, a slip-off preventive pin as well as a cam pin are formed in a lens barrel, a cam groove and a slip-off preventive groove that are to be engaged with the respective pins are formed in a movable cam ring, and a first projection is formed on one side of the slip-off preventive groove in a direction of an optical axis. With this arrangement, the slip-off preventive pin comes into abutment with the first projection during extension of a zoom lens so that the cam pin can be prevented from slipping off the cam groove.
However, according to the technique described in Japanese Laid-Open Patent Publication (Kokai) No. 2005-128188, the cam groove and the slip-off preventive groove are identical in shape, and also, the cam groove and the slip-off preventive groove are formed as separate grooves independent of each other.
Thus, according to the technique described in Japanese Laid-Open Patent Publication (Kokai) No. 2005-128188, the cam groove and the slip-off preventive groove must be spaced out in the direction of the optical axis in order that the lens barrel can move in synchronization in the direction of the optical axis, in other words, in order that cam paths can be the same.
For this reason, according to the technique described in Japanese Laid-Open Patent Publication (Kokai) No. 2005-128188, the movable cam ring is long in the direction of the optical axis, and this presents an obstacle in miniaturizing the lens barrel, and by extension an optical apparatus such as an image pickup apparatus having the lens barrel.